Recent advancements in solar collector-evaporator for direct expansion solar heat pump

The direct expansion solar heat pump (DX-SHP) is a competent and sustainable option for domestic heating and drying applications. The solar collector-evaporator is a vital component of DX-SHP, which operates on solar energy and low-temperature ambient energy. The heat collection capacity, coefficient of performance, and evaporation temperature are used to quantify its performance. In this context, a systematic literature review on recent advancements in the collector-evaporator of DX-SHP is presented. This paper highlights and discusses the various configurations of solar collector-evaporators, theoretical and experimental investigations, and the selection method of eco-friendly refrigerants. The impact of different performance factors, such as ambient conditions, structural parameters, and types of refrigerants, on solar collector-evaporators is also reviewed. The optimal range for solar radiation, wind speed, and temperature is found to be 350 W/m2-700 W/m2, 0.5 m/s -2.5m/s, and 5°C to 35°C. The DX-SHP system produces hot water from 15°C to 60°C, with an average COP of 1.5 to 4.5. The finned solar collector-evaporator with R290 refrigerant performs optimally in various climatic conditions. Integrating solar collector-evaporators with innovative technologies such as microchannel, heat pipe, thermoelectric generators, and photovoltaic thermal collectors with compound parabolic and Fresnel lenses can improve the system's performance. In this review, researchers can find scope for performance enhancement of the collector-evaporator used in DX-SHP.